Rotary Joint for Transferring Melted Plastic from an Extruder to Molds of a Rotary Machine for Molding Preforms

ABSTRACT

A rotary joint for transferring melted plastic from at least one extruder to a plurality of molds of a rotary machine for molding preforms, the joint comprising a fixed structure ( 3 ′) provided with a fixed longitudinal element ( 23 ) therein, defining a longitudinal axis (Y), and a movable structure ( 3 ″) which can rotate about said axis (Y) and is adapted to be integrally fixed to the rotary machine; wherein a first passage channel ( 11 ) is provided within said fixed element ( 23 ); wherein a second passage channel ( 11 ′) is provided within said movable structure ( 3 ″) and coaxial to said first passage channel; said second passage channel ( 11 ′) being in communication at a first end thereof with said first passage channel ( 11 ), and being in communication at a second end thereof with a plurality of lateral radial channels ( 52 ) provided within said movable structure ( 3 ″); wherein there is provided, between the fixed structure ( 3 ′) and the movable structure ( 3 ″), a gap in which a spiral seal ( 24 ) is arranged for ensuring the action of sealing the melted plastic between said fixed structure and said movable structure.

FIELD OF THE INVENTION

The present invention relates to a rotary joint for transferring meltedplastic from an extruder to molds of a rotary machine for moldingpreforms made of thermoplastic material, e.g. PET, by means ofinjection-compression, intended to manufacture food-grade containers,especially bottles.

STATE OF THE ART

The production of very high numbers of thermoplastic containers, inparticular of bottles, is a process which, starting from the rawmaterial, generally polyethylene terephthalate or PET, allows to obtainfinished containers of even particularly complex shape which are suitedto the most varied market needs, and which are particularly light andstrong even when subjected to heavy pressure at ambient temperature. Thetransition of PET in raw state in the form of granules to plasticcontainer can be carried out either by means of a one-stage process orby means of a two-stage process, as desired.

The one-stage process is carried out using a single plant in which thetransition of PET from granules to preform, by means of a step ofinjecting into molds, and the transition from preform to plasticcontainer, by means of a step of stretching-blowing, occur continuouslywithout the preform being allowed to cool down completely up to ambienttemperature. The preform thus still preserves part of the latent heatremaining from the step of injecting, with a considerable saving ofenergy, because the preforms require less heat to be returned to thesuitable blowing temperature with respect to the case in which they mustbe heated starting from ambient temperature.

A so-called two-stage process instead is carried out in two plants whichare generally but not necessarily separate: one plant carries out thefirst part of the container manufacturing process with the transition ofPET in granules to preform, i.e. carries out the step of injecting thePET preforms in injection molds. The second part of the process, whichtransforms the preform into the final container in a blower using thestretching-blowing technique, which is generally used today for blowingPET containers, is carried out in the second plant. The two-stageprocess may also be carried out in the same plant, which includesinjecting the preforms and blowing them into bottles, but the twooperations are carried out in two distinct times. The preforms areallowed to cool down after injection to reach ambient temperature. Next,when the preforms must be transformed into finished containers, inparticular bottles, they must be heated in appropriate ovens to takethem back to the temperature required for the blowing process typical ofthe thermoplastic used or necessary for stretching-blowing, if PET isused.

One reason for preferring an integrated one-stage plant is that a plantof this kind ensures a better finished product quality with lessconsumption of energy, as previously mentioned. The better quality ofthe finished product is allowed by the possibility of modifying theproduction parameters in real time, adapting them to the manufacturingneeds of the containers in a quick and effective manner. Furthermore, inan integrated one-stage plant, a preform manufacturing error can beimmediately detected thus allowing to correct faults of the preformand/or the finished container.

In two-stage plants, instead, a fault occurring on preforms during theinjection operation may be detected with a delay such to compromiseseveral days of production. Moreover, the lack of continuity between thetwo stages prevents all the information of the preform lifecycle frombeing stored, whereby the step of stretching-blowing occurs withoutknowing the exact features of the processed preforms at any time. Notless important is the problem that results from the preformcontamination when these are not immediately transformed into finalcontainers, if these are intended to contain a food-grade product, thuscompromising the shelf-life thereof.

Blowing molding is preferred today also because it is particularlysuited for making hollow bodies with a complex shape and many undercuts.Blowing has the great advantage of allowing the production of containerswith a body which is much wider than the mouth, such as bottles andflasks. Furthermore, it is preferred over rotational molding because theproduction cycle, i.e. the cycle time, is shorter. Blowing is aparticularly fast, efficient production process adapted to masscontainer production, such as thermoplastic resin bottles, and inparticular PET for beverages, for which the market demands particularlyhigh manufacturing numbers. Short cycle times allows to distribute theplant cost on a very high number of pieces, thus allowing to achieveproduction rates even in the order of several tens of thousandcontainers per hour in the larger blowing plants. A key element from theeconomic point of view is thus the cost of the raw material, e.g. PET,PE, PPE, PP, and thus the reduction of the amount of material used tomanufacture a single container is crucial.

One of the problems still to overcome in the making of one-stage plantsis their low production rate compared to two-stage plants, because thefirst part of the container manufacturing process, which is the preforminjection process in multiple cavity molds, today the most common, isslower than the second part of the manufacturing process, which is thestretching-blowing process, whereby the latter operation, in which veryhigh production capacities may be already achieved, must run withproduction capacities which are lower than the maximum capacity tomaintain it at the same level as that of the preform injection mold.

A variant of the described technique, which appears most promising fromthe point of view of production capacity and produced preform quality,is the use of the injection-compression technology which requires lesspower to work and lower press tonnage for compressing the preform mold.Another advantage of this process is that it subjects the thermoplasticmaterial to a lower stress, allowing to manufacture final containerswith very thin walls, while ensuring a high container quality. If arotational platform is used to implement the injection-compressionproduction cycle instead of an alternating cycle typical of theinjection presses, it is easier to integrate the preform molding machinewith a rotational blower for blowing the containers if an integratedone-stage plant is used.

It is thus felt the need to provide new rotational injection machinesfor making thermoplastic preforms, in particular made of PET, to complywith the market demand to increase productivity and reduce the cost ofpreforms without reducing their quality. Solutions have thus been soughtto increase the speed of a preform injection-compression machine withoutdecreasing the quality of the manufactured preforms. Furthermore, theneed to increase automation and reduce maintenance times in theinjection-compression machines for thermoplastic containers is alsofelt. The problem of transferring the melted plastic from the extrusionmodule to the molding cavities exists in a high-productioninjection-compression rotary platform. WO2011161649 describes a rotaryjoint for transferring melted plastic from an extruder to the molds of arotary molding machine. The rotary joint essentially consists of twoparts: a fixed part and a rotating part, defined in the wheel at theperiphery of which the molding cavities are arranged, such a rotatingpart comprising a labyrinth seal. The main drawback of such a joint isidentified in that it is not an element per se but one part (therotating one); it is an integral part of the wheel, which impliesmaintenance problems. It is thus felt the need for a rotary joint whichovercomes the aforesaid drawbacks. A further need is to ensure anoptimal sealing of the melted plastic during the rotary movement of thecarousel, thus avoiding leakages of said plastic from the rotary jointas much as possible.

SUMMARY OF THE INVENTION

It is the object of the present invention to provide a rotary joint fortransferring melted plastic from an extruder to the molds of a rotarymolding machine of thermoplastic preforms, in particular PET preforms,which contributes to increasing the global productivity of the preformmanufacturing plant.

It is a further object of the present invention to provide a rotaryjoint which is highly effective in preventing leakages of melted plasticduring the rotary motion of the carousel onto which the preform moldsare fixed.

The present invention aims to achieve the aforesaid objects by means ofa rotary joint for transferring melted plastic from an extruder to themolds of a rotary preform molding machine which, according to claim 1,comprises:

-   -   a fixed structure provided with a fixed longitudinal element        therein, defining a longitudinal axis Y,    -   and a movable structure adapted to rotate about said        longitudinal axis Y and adapted to be integrally fixed to the        rotary machine, wherein a first passage channel is provided        within said fixed longitudinal element,        wherein there is provided a second passage channel within said        movable structure and coaxial to said first passage channel,        said second passage channel being in communication with said        first passage channel at a first end thereof, and being in        communication with a plurality of lateral radial channels at a        second end thereof, said lateral radial channels being provided        within said movable structure,        wherein, between the fixed structure and the movable structure,        a gap is provided in which a labyrinth seal is arranged for        ensuring the action of sealing the melted plastic between said        fixed structure and said movable structure.

By virtue of the features of the invention, a rotating carousel can beprovided containing the preform injection molds in groups of two, threeor four, offering the following advantages:

-   -   higher container production rates because the carousel can be        rotated at higher rotation speeds, with respect to plants having        molds arranged in a different manner, by virtue of the        innovative rotary joint for the melted resin distribution;    -   a reduced mechanical cycle time for opening and closing the        injection-compression mold;    -   reduction of downtime for format change;    -   possibility of using robotized systems for disassembling and        refitting the machine or subgroups thereof by virtue of the        apparatus architecture modularity;    -   the possibility of obtaining high quality preforms and reducing        the manufacturing waste by virtue of the resin dosing accuracy        provided by the apparatus when dispensing the resin into each        mold;    -   a better centering of the mold punch in the molding cavity with        the result of improving the molded preform concentricity;    -   release from deformations caused by thermal expansion and from        typical mechanical constraints of multiple cavity structures.

The resulting global advantage is higher hourly productivity rate ofbetter quality preforms.

The dependent claims describe preferred embodiments of the inventionforming an integral part of the present description.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features and advantages of the present invention will becomeapparent in the light of the detailed description of preferred, but notexclusive, embodiments of an injection-compression apparatus,illustrated by way of non-limitative example, with the aid of theaccompanying drawings, in which:

FIG. 1 is a diagrammatic plan view of a thermoplastic preformmanufacturing plant in which the rotary joint according to the inventionis incorporated;

FIG. 2 is a partial axonometric view of the plant in FIG. 1;

FIG. 2 a is a partial side view of the plant in FIG. 1;

FIG. 3 is a section view along an axial plane of a part of the plant inFIG. 1 comprising the rotary joint according to the invention;

FIG. 3 a is an enlarged section view of the rotary joint according tothe invention;

FIG. 3 b is an axonometric view of an enlarged detail of the rotaryjoint in FIG. 3 a;

FIG. 4 is an axonometric view of an element of the plant in FIG. 1;

FIG. 5 is a side section view of the element in FIG. 4;

FIG. 6 is an axonometric view of another element of the plant in FIG. 1;

FIG. 7 a is a section view of the element in FIG. 6 in a first operatingposition;

FIG. 7 b is a section view of the element in FIG. 6 in a secondoperating position;

FIGS. 8 and 9 are axonometric views of another enlarged element of theplant in FIG. 2 in two different operating positions;

FIGS. 10 and 11 are axonometric views of another enlarged element of theplant in FIG. 1 in two different operating positions;

FIGS. 12 a, 12 b, 13 a and 13 b are section views of a thermoplasticmaterial injection block incorporated in the plant in FIG. 1 in thevarious operating positions;

FIGS. 14, 15, 16 and 17 are section views of an element of the plant inFIG. 1 in different operating positions.

The same reference numbers and letters in the figures refer to the samemembers or components.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION

A preferred embodiment of an injection-compression apparatus forthermoplastic resin containers is described below with particularreference to the aforesaid figures.

FIG. 1 is a diagrammatic plan view of an injection-compression plant ofthe rotational type, for thermoplastic material containers, typicallyPET preforms for the production of bottles or other containers for foodor non-food use.

In this diagram, the injection-compression apparatus is associated witha preform cooling device 51, e.g. with a star conveyor 50, provided withgrippers 4, for transferring the preforms from a rotating carousel 2 tothe cooling device 51. Such a configuration is typical in a containermanufacturing plant of the two-stage type. A person skilled in the artwill appreciate that, without departing from the scope of the invention,instead of the preform cooling device 51 a blowing machine can beassociated with the injection-compression apparatus, with thecorresponding accessory devices of the type known in the art, such aspreform transfer, cooling and/or conditioning wheels, heating ovens etc.. . . If needed, other machines, for example used to label thecontainers and fill them with the intended product, may be inserted inthe plant.

Furthermore, various plant components can be arranged in a relative planposition either aligned or grouped with the rotation axes which ideallyform a triangle or, more in general, a polygonal to adapt to the spaceoccupation needs of the place where the plant is installed.

The plant in FIG. 1 comprises at least one extruder 1, of known type,the function of which is to plasticize the polymer transforming it fromthe granular solid state to the fluid state, with the contribution ofenergy provided by specific heaters and by friction forces which aregenerated due to the action of the extruding screw, thus producingmelted resin.

The plant also comprises the rotating carousel 2 for preforminjection-compression molding with can rotate about a vertical axis Y.

A distribution device 3 for distributing the melted resin produced byextruder 1 up to each mold, arranged on the outer periphery of carousel2, is provided between the extruder 1 and the rotating carousel 2. Asthe injection-compression apparatus is configured as a rotating carousel2, the flow rate of melted resin to be supplied must be nearly constantover time, whereby an extruder 1 capable of generating a constant flowrate must preferably be used.

The rotating carousel 2, with particular reference to FIG. 2, comprisesa horizontal lower disk 20 and an upper disk 22 parallel to the lowerdisk. Both disks 20 and 22 share the same rotation axis Y, forming anassembly with the ideal shape of a drum. A plurality ofinjection-compression molds 9′, 9″, 9′″ is arranged along the peripheryof the drum, the molds having a substantially elongated shape and eachdefining a vertical sliding axis Y′ (FIG. 4) of the half-molds parallelto the rotation axis Y of carousel 2, and which may rotate, for example,in the direction of arrow F (FIG. 2) or if needed in the oppositedirection.

The lower disk 20 and the upper disk 22 are joined to each other by themolding modules 9 so as to contribute to forming the load-bearingstructure of the carousel 2 having a high rigidity, and thus capable ofwithstanding the high loads which are generated during theinjection-compression process. The number of injection-compression moldsis defined during the step of designing the injection-compressionapparatus according to criteria related to the intended productivityrate of the preform and/or finished container manufacturing plant.

Only two molding modules 9, each comprising three injection-compressionmolds 9′, 9″, 9′″, are shown in FIG. 2, for reasons of clarity of thedescription, but is understood that the entire periphery of the carousel2 is occupied by the molds 9′, 9″, 9′″, perfectly equal to one anotherand divided into a number of modules 9 which is three times lower thanthe number of molds.

In particular, the solution in FIG. 2 shows an embodiment with moldingmodules 9 with three molds 9′, 9″, 9′″ along the peripheral surface ofthe carousel 2; however, modules with a number of molds other than threecan be made without departing from the scope of protection of theinvention. These solutions are not shown in the figures because they canbe easily understood by a person skilled in the art.

A melted resin distribution device 3, shown in greater detail in FIGS.3, 3 a and 3 b, is provided in the middle of the carousel 2 at the lowerdisk 20. The distribution device 3 allows to transfer the melted resinfrom the single feeding conduit 10 of the fixed extruder 1 to theplurality of molding modules 9 which rotate together with the carousel2.

Advantageously, the distribution device 3 is provided with a rotaryjoint, which is the object of the present invention, comprising:

-   -   a fixed structure 3′ centrally provided with a longitudinal        fixed element 23 therein, which extends along axis Y, in which        there is provided a passage channel 11 of the melted resin        having an appropriate diameter, compatible with the necessary        flow rate of melted resin, from 28 to 42 mm, preferably of 32        mm;    -   and a movable structure 3″, in turn comprising:        -   a first central rotary element 25, arranged in the upper            part of the distribution device 3, above said longitudinal            fixed element 23, and integrally fixed to the lower disk 20            of the carousel 2;        -   a second central rotary element 102, substantially            bell-shaped (FIG. 3 b), arranged under the first rotary            element 25 and integrally fixed thereto, provided with a            central through cavity, having a cylindrical shape, crossed            by the upper portion of the central fixed element 23.

A melted resin passage channel 11′ is provided in the first rotaryelement 25, having the same diameter as the passage channel 11 at afirst end thereof and communicating with the latter. The passagechannels 11 and 11′ are arranged along the Y axis of the carousel 2; thepassage channel 11 being considerably longer than the passage channel11′. Said passage channel 11′ is instead provided at a second endthereof with a flaring for connecting to a plurality of radial lateralchannels 52, again provided inside said first rotary element 25.

Since, during the rotation of the rotary carousel 2, the melted resintends to partially exit from the gap between the fixed structure 3′ andthe movable structure 3″ when the resin passes from channel 11 tochannel 11′, a spiral seal 24 advantageously ensures the tightness ofthe melted resin between said fixed structure 3′ and said movablestructure 3″.

The spiral seal 24 is obtained in the space between the inner surface101 of the cylindrical through cavity in the middle of the second rotaryelement 102 (FIG. 3 b), integral with the first rotary element 25, andthe smooth outer surface of the fixed longitudinal element 23. A single-or multi-start spiral groove 103, e.g. with two or four starts, isadvantageously provided on the inner surface 101. The spiral groove 103is a helical groove having the helix inclined in the direction oppositeto that of rotation of the rotary elements 25 and 102, and thus of theentire carousel 2, whereby the rotary relative motion of the spiralswith respect to the fixed longitudinal element 23 creates a pumpingeffect which opposes the release of pressurized melted resin from thegap between the fixed structure 3′ and the movable structure 3″,pressing it upwards and maintaining it within the distribution device 3itself.

In particular, such an inclined helix is such to oppose to the naturalexiting direction of the flow of melted plastic into the gap with itsrotary motion. For example, in the case of rotation of the movablestructure 3″ according to direction F (FIG. 2) the spiral groove 103 isa left-handed helix.

The helix of the spiral groove 103 is advantageously inclined by anangle no greater than 45° with respect to a plane orthogonal to thelongitudinal axis Y, in order to make the aforesaid pumping effect moreeffective. Good results have been empirically found with an angle from10° to 40°. Further investigations have indicated excellent results withan angle from 15° to 30°.

Moreover, the best operation of the spiral seal of the rotary joint ofthe invention has been found when the spiral groove 103 is made on theinner surface 101 of the second rotary element 102 and when,advantageously, between the crests of the spiral and the smooth outersurface of the fixed longitudinal element 23 there is a distance of atleast 2 mm, preferably from 3 to 6 mm. Optimal results have beenempirically found with a value of said distance of about 4 mm. Thissolution allows to work at the maximum molding speed of the machine inthe case of thermoplastic material, such as for example PET,polypropylene and polyethylene, while taking the viscoelastic propertiesof these materials into account.

In particular, the gap between fixed structure 3′ and movable structure3″ has an annular shape, with L-shaped cross section, and is delimitedon one side by the lower surface of the first rotary element 25 and bythe upper surface of the longitudinal fixed element 23, and is delimitedon the other side by the inner surface 101 of the rotary element 102 andby the smooth outer surface of the fixed longitudinal element 23.

This rotary joint allows the mutual relative rotary union between thelongitudinal fixed element 23 and the first rotary element 25. On theother hand, the fixed element 23 is fixed to a supporting element 35,which connects to the structure of the plant. A thrust bearing 26 isinterposed between the upper movable structure 3″, rotating about the Yaxis, and the lower fixed structure 3′ of the distribution device 3.

The upper surface 110 of the second rotary element 102 is advantageouslyshaped as a circular crown (FIG. 3 b) and is provided with a pluralityof radial grooves 111, equally spaced apart one from the next. Thisdesign allows the contact seal between the second rotary element 102 andthe first rotary element 25 to be improved.

The melted resin, coming from the feeding conduit 10 of extruder 1,passes in sequence into the passage channel 11, into the passage channel11′ and into the lateral radial channels 52. Said lateral radialchannels 52 of the first rotary element 25, in turn, communicate withthe respective lateral conduits 27 which connect the first rotaryelement 25 to the respective molding modules 9.

Each lateral conduit 27 is provided with a respective central channel27′, having a suitable diameter for feeding the injection-compressionmolds 9′, 9″, 9′″ with a predetermined amount of melted thermoplastic.Electric resistors 38′, 38″ and 38′″, adapted to maintain the meltedresin at a correct temperature so that the resin can reach the modules9′, 9″, 9′″ at the design temperature for preform molding, areadvantageously arranged along the various conduits crossed by the meltedresin inside the distribution device 3.

Each central channel 27′ of the lateral conduits 27 is connected to amanifold 28 (FIGS. 12 a, 12 b, 13 a, 13 b), obtained on the injectionblock 29, which by means of an appropriate channeling circuitcommunicates with the respective molding cavities 41′, 41″, 41′″arranged on corresponding molding module 9. Although reference is madein this part of the description for the sake of brevity to a singlemolding module 9 provided with three molds 9′, 9″, 9′″ and, in detail,to a single mold 9′, it is understood that all the molds and the moldingmodules which are included in the rotary carousel 2 have the samefunctional and structural features, unless specified otherwise. In theembodiment shown here, the plurality of molding modules 9 is in numberequal to one third of that of the molding cavities 41′, 41″, 41′″.

The molding module 9 is thus described in greater detail with referencein particular to FIGS. 4 and 5. The molding module 9 comprises asupporting element, e.g. in the form of a frame 21 with very solid,rigid, substantially C-shaped, structure, which is fixed integrally onthe upper part thereof to the upper disk 22 and on the lower partthereof to the lower disk 20. Its rigidity allows to contrast thereaction forces produced by the forces associated with theinjection-compression molding operation. Three molds 9′, 9″, 9′″, whichare mutually equal and form the module 9, are fixed on the open part ofthe frame 21 facing in radial direction towards the outside of thecarousel 2.

The mold 9′ consists of three parts: the upper part 12, the central part13 and the lower part 14.

For reasons of clarity, the upper part 12 is conventionally the part ofthe mold 9′ which remains connected to the frame 21 of the module 9during the current maintenance operations or format change operations ofthe molding cavity 41′.

The central part 13 is conventionally the part of the mold 9′ which canbe replaced with a relatively simple, rapid operation when it must bereplaced for reasons of wear or format change of the preforms to bemanufactured. The central part 13, during the current moldingoperations, remains fixed and integral in block with the upper part 12and both parts 12 and 13 move together along direction D (FIG. 5) toclose and open the molding cavity 41′.

The lower part 14 is conventionally the part of the mold 9′ integrallyfixed to the frame 21, which does not move during the current moldingoperations and can be replaced by a relatively simple, rapid operationwhen the molding cavity 41′ needs to be replaced for reasons of wear orformat change of the preforms to be manufactured.

The upper part 12 comprises a longitudinal rod 55 sliding vertically ina hole-guide of the upper part of the frame 21, and integral on theupper end thereof with a runner 53 which can slide in the direction ofthe arrow D along the guide 54 integrally fixed to said upper part ofthe frame 21. The rod 55 includes a wheel 230, or equivalent element,which acts as a tappet capable of following a cam surface (not shown),which controls the vertical movement of the upper part 12 and centralpart 13 of the mold 9′ during the molding operation.

A blocking and unblocking wedge 57 for blocking or unblocking the rod55, controlled by a pneumatic actuator 58, allows to keep the upper part12 and the central part 13 fixed in a lowered position (FIG. 14), byacting on a further wheel 56 provided on the rod 55, during the step ofmolding the preform. When the wedge 57 is instead retracted from thespecific seat in the rod 55 under the action of the pneumatic actuator58 (see position in FIGS. 5, 15, 16 and 17), it allows the verticalsliding of the upper part 12 and central part 13 to perform other stepsof the molding cycle, described below.

The central part 13 comprises (FIGS. 6, 7 a, 7 b):

-   -   a bayonet coupling 15 to join to the upper part 12, so as to        allow a quick attachment and detachment of the central part 13        from the upper part 12, e.g. during preform format change        operations;    -   a sliding guiding cage constituted by four rods 16′, 16″, 16′″,        16 ^(iv), associated with respective return springs 200 and        fixed on the upper part to a first plate 18 and on the lower        part to a base structure 18″, the first plate 18 being provided        with a central through hole 210 through which the rod 55 passes,        the rod being connected at the lower end thereof to the bayonet        coupling 15 provided inside the guiding cage, allowing a        relative sliding movement between the bayonet coupling 15 and        the first plate 18;    -   a pneumatic cylinder 19 having an inner cavity, defining a        pneumatic chamber in which a piston 49 is accommodated, said        cylinder 19 being fixed by an upper end thereof to the bayonet        coupling 15, possibly with an interposed extension 220, and        being provided at a lower end thereof with a flat part, e.g. in        the shape of a second plate 18′, preferably coinciding with the        same flat lower end of the cylinder 19 itself, sliding along the        four rods 16′, 16″, 16′″, 16 ^(iv); said return springs 200,        helical and coaxial to said rods, being fixed at a first end        thereof to the first plate 18 and at a second end thereof to the        second plate 18′, either integral with or belonging to part of        the cylinder 19, which can move parallel with respect to the        first plate 18;    -   a punch or core 59, fixed integrally to the piston 49, which        forms a component complementary to the molding cavity 41′ to        complete the mold of the preform, delimiting the inner shape of        the preform;    -   cams 8′, 8″, fixed integrally to the guide element 59′ of the        punch 59, external and coaxial to the latter;    -   the base structure 18″, to which the four rods 16′, 16″, 16′″,        16 ^(iv) are fixed, comprising a system of two lateral levers        (or rocker arms) 67′, 67″, hinged on respective pins 68′, 68″ of        the base structure 18″ and onto which respective tappets 69′,        69″ are fixed which follow the cams 8′, 8″; said levers 67′, 67″        control the opening and the closing of two half-lips or        half-collars 66′, 66″ (FIGS. 7 a and 7 b) which define, when        close (FIG. 7 a), a collar defining the negative cavity which        molds the neck zone of the preform, allowing to complete the        closing of the molding cavity 41′ when the preform must be        molded.

A spring 63, inside the cylinder 19, produces a slight thrust on thepunch 59 to promote a regular filling, by the melted resin, of themolding cavity 41′ during a first step of molding. The bayonet coupling15, shown in greater detail in FIGS. 10 and 11, comprises a sleeve 60arranged about a clutch base 61 with a constraint which allows anangular rotation thereof about the axis Y′, but is integral in thedirection parallel to the axis Y′ with the clutch base 61. The sleeve 60is provided with teeth 62′, 62″, 62′″, directed towards the interior ofthe cavity thereof, which are shaped to be inserted into correspondinglongitudinal grooves of the longitudinal rod 55 and slide into anannular groove of said longitudinal rod 55 with a relative rotation ofabout 60° between rod 55 and sleeve 60 in the direction of the arrow R.Thereby, it is possible to attach and detach the central part 13 fromthe upper part 12 of the mold 9′ rapidly in order to carry outassembly/disassembly operations or to change the preform format.

The lower part 14 of the mold 9′ comprises the molding cavity 41′ and asecond bayonet coupling 64′ (FIGS. 8, 9), provided on the supportingframe 21, which cooperates with a corresponding clutch 65 (FIGS. 6, 7 a)arranged at the base of the cavity 41′. Thereby, the replacementrapidity of the cavity 41′ is ensured for maintenance or for formatchanging.

It is worth noting that in order to ensure a format change comprising ahigher number of preform lengths the rod 55 must be provided with atleast one extension, which may be either added or removed to reach thenecessary length. Alternatively or in combination, said at least oneextension 220 may be arranged between the bayonet coupling 15 and thecylinder 19 (FIGS. 6 and 7).

When the cavity 41′ is opened, the central part 13 moves away from thelower part 14 upwards in the direction indicated by D. Once the firstplate 18 abuts, by means of the bumper 17, preferably made of rubber,against the upper part of the C-shaped frame 21, the rod 55 is raisedfurther by means of the cam surface acting on the wheel 230, thus movingthe punch 59 and consequently the cams 8′, 8″ upwards by a relativemotion with respect to the pierced plate 18, which at that time remainsstationary together with the base structure 18″, and thus together withthe fulcrums 68′, 68″ which maintain the levers or the rocker arms 67′,67″ at the same predetermined distance from the pierced plate 18.

The relative movement of the cams 8′, 8″ and the levers 67′, 67″separates the two half-collars 66′, 66″ (FIG. 7 b) with respect to eachother by virtue of the fact that the tappets 69′, 69″ of the levers 67′,67″ follow the profile of the cams 8′, 8″, releasing the neck of thepreform, which may be extracted from the punch 59 by using specificgrippers provided on the transfer star conveyor 50. The return springs201 (FIG. 7 a) keep the tappets 69′, 69″ into contact with the cams 8′,8″. The description made for the mold 9′ is repeated in similar mannerfor the molds 9″ and 9′″ of the molding module 9 and is omitted for thesake of brevity of the description.

The injection block 29 is described in greater detail with reference toFIGS. 12 a, 12 b and 13 a, 13 b, which show the steps of loading of theresin dose and the steps of filling of the molding cavity 41″ with theresin dose for each molding cycle, respectively. Although reference ismade to a molding cavity 41″, it is apparent that the block 29 has othertwo molding cavities 41′ and 41′″, perfectly equal to the cavity 41″with the same accessory components described for the cavity 41″ andwhich are filled at the same time.

The resin is injected into the molding cavity 41″ by means of the thrustof a piston 39 sliding in the respective dispensing injector 34connected to the hot chamber 30. The piston 39 is actuated by apneumatic cylinder 33, which is controlled in turn by a valve (not shownin the figures). Where necessary, appropriate heating means, e.g.resistive bands, are provided to maintain the resin at the designtemperature in the various parts of the injection block 29.

An injection nozzle 31 is arranged at the top of the hot chamber 30 witha vertical axis Y′ thereof and is also heated by an electrical resistor,e.g. of the band type. Such an injection nozzle 31 allows the dose ofmelted material to pass into the molding cavity 41″ through the hole 42.Preferably, said hole 42 has a diameter of 3-5 mm, preferably of 4 mm.

The hot chamber 30 is crossed by a first conduit 70 connected to themanifold 28 which receives the resin from one or more lateral conduits27. This first conduit 70 communicates with a second conduit 71, alsowithin the hot chamber 30 and connecting the tank 72 of the dispensinginjector 34 with the injection conduit 73 of the injection nozzle 31.The hole 42 is either opened or closed during the operations by means ofa shutter 32.

Advantageously, a mechanism with a single actuator for the fillingoperation of the respective molding cavity and the filling operation ofthe respective dispenser 34 is provided for each molding cavity 41′,41″, 41′″ of each module 9. However, in this embodiment, there is onlyone electrovalve which controls the three pneumatic cylinders 33, and sothe three molding cavities 41′, 41″, 41′″ of each module 9 carry out thesame step of each work cycle at the same time. The mechanism whichactuates the switching between the step of filling the dispenser 34 andthe step of filling the molding cavity can be a valve 36, e.g. of thespool or shutter type, capable of either opening or closing the passageof melted resin from the conduit 70 towards the tank 72 for filling thedispensing injector 34. Said valve 36 is actuated by means of anactuation device 37, arranged at a first end of the valve 36. Theshutter 32 is integrally connected to a second end of the valve 36,opposite to the first end. The actuation device 37, the valve 36 and theshutter 32 are arranged longitudinally and preferably along a same axisY′.

The actuation device 37 comprises two separate cylindrical chambers 74,75 provided with respective pistons 76, 77 integral with each other. Thelower cylindrical chamber 75 is provided with two compressed airinlet/outlet conduits 78,

An adjustment ring nut 44 of the position of the abutment plate 43 ofthe dual-acting piston 40 to adjust the weight of the melted resin doseaccurately, also to the hundredth of a gram, is provided on the bottomof the cylindrical chamber of the pneumatic cylinder 33 of thedispensing injector 34. The position of said abutment plate 43 can beset singularly for a better preform calibration.

The dual-acting piston 40 of the pneumatic cylinder 33 is actuated by acombination of pressures and counter-pressures generated by thecompressed air introduced into the upper 45 and lower 46 chambers and bythe melted resin coming from the extruder 1 by means of the channel 70of the hot chamber 30. During the step of loading the resin in thedispenser, corresponding to the descent of piston 40 along the directionshown by arrow G, the pressure of the melted resin pushed by theextruder into tank 72 operates on the piston 39 and prevails withrespect to the combination of the compressed air pressures introducedinto the upper chamber 45, appropriately adjusted in the range from 10to 40 bar, and into the lower chamber 46, always connected to the aircircuit preferably at 40 bar.

During the step of injecting the melted resin, corresponding to araising of piston 40 along the direction indicated by G, the highpressure compressed air, preferably at 40 bar, works in the lowerchamber 46, coming from the inlet fitting 48, while the upper chamber 45of the same cylinder 33 is connected by means of a control valve to thelow-pressure (0-8 bar) air recovery circuit by means of the outletfitting 47.

The coordinated movement of the valve 36, of the shutter 32 and of thedispensing injector 34, as well as the calibration of the abutment plate43, allows to dose the amount of melted resin needed to be introducedinto the molding cavity 41″ accurately according to the design of thepreform to be manufactured. The coordinated movement of the injectionblock is actuated by using electrovalves driven by programmable systems.

In particular, the valve 36 is opened by means of the actuation device37, leaving the conduit 70 open, when the piston 39 of the dispensinginjector 34 is in advanced position, as shown in FIG. 12 a. The openingof the valve 36, by means of its upward displacement, determines theclosing of the hole 42 of the injection nozzle 31 by means of theshutter 32 and a retraction of the dual-acting piston 40 of thedispensing injector 34 under the action of the pressurized melted resinfront coming from the hot chamber 30 and which fills the tank 72.

After the dual-acting piston 40 reaches the abutment plate 43, the stepof loading is completed and the dispensing injector 34 is ready toinject the dose into the molding cavity 41″, as soon as the respectivecommand is imparted.

The step of injecting includes the closing of the valve 36, by means ofa downward displacement thereof determined by the actuation device 37,and the simultaneous opening of the shutter 32, which moves down thusreleasing the outlet section of the nozzle 31 (FIG. 13 a), i.e. the hole42, and the subsequent injection movement of the dispenser 34 by meansof the dual-acting piston 40 (FIG. 13 b). The valve 36 is closed duringthe advancement of the piston 39 of the dispensing injector 34, andtherefore the melted resin is forced to pass through the conduit 71 andthe injection conduit 73 to reach the interior of the molding cavity41″.

Each lateral conduit 27 is provided with two spherical joints 203 (FIG.3 a) on the ends, by means of which it is connected to the manifold 28on one side and to the rotary element 25 on the other side in order toallow to compensate the relative displacements between lower disk 20 andthe rotary element 25 of the distribution device, mainly due to thermalexpansions, by means of a rotary displacement. In a top plan view (notshown), the lateral conduit 27 is arranged not precisely aligned inradial direction with respect to the rotation axis Y, instead it isarranged slightly offset with respect to the axis Y, i.e. the ideal axisof the conduit 27 ideally never intersects the centre of rotation of thecarousel 2, but the ideal line that it defines passes at a predetermineddistance from this centre. This arrangement (shown in FIG. 2) allows totake into account the thermal expansions of the lateral conduit 27 bothin radial and in vertical sense. Such a arrangement, as explained above,is the same for each lateral conduit 27 of each molding module 9 of thecarousel 2. In an alternative variant, each molding module 9 may includeas many lateral conduits 17 as the molds in the module.

According to a preferred variant of the rotary carousel 2, extruder 1acts as a volumetric pump to provide the flow rate of melted resinrequired at an outlet pressure preferably between 50 bar and 200 bar.Such a pressure is sufficient to move the melted resin inside the entireinternal channeling of the distribution device 3, of the lateral conduit27 of each molding module 9, of the respective hot chambers 30,considering that the single passage channel 11 in the distributiondevice 3 can feed three dispensing injectors at each molding cycle ineach molding module 9.

A preferred maintenance temperature of the melted resin inside thevarious channelings is 270° C. and is ensured by means of controlledelectric resistors arranged in the points where needed. Given thisworking temperature of the resin, the distribution device 3 iswater-cooled to maintain the temperature of the thrust bearing 26 atless than 80° C. Furthermore, all the resin distribution system ispreferably externally coated with an insulating material to limit theundesired heat loss and improve the energy efficiency of the entireplant.

The transfer star conveyor 50 transfers the manufactured preforms, bymeans of a plurality of grippers 4 fixed to the transfer star conveyor50, in sequence from the rotary carousel 2 to the preform cooling device51, where they are either cooled or thermally conditioned (FIG. 1).

The molding process comprises a sequence of steps which are carried outat the same time in the three molding cavities 41′, 41″, 41′″ of themodule 9.

The first step (FIG. 14) is the step of molding the preforms duringwhich a downwards movement of rod 55 in direction D, which controlspunch 59, is performed. The mold 9′ is blocked by the pneumatic wedge 57and the high pressure air, in the order of 30-35 bar, is inserted in thecompensation chamber 94 of the cylinder 19. The melted resin inside thecavity 41′ is thus subject to the maintenance pressure, which depends onthe ratio of the areas of the compensation chamber 94 and the punch 59.The thermal cooling is carried out with refrigerated water which runs inthe conduits provided for this purpose in the mold elements in contactwith the resin, i.e. cavity 41′, punch 59 and half-collars 66′, 66″.During this step the volume recovery due to the variation of density bythermal effect is also performed by the lowering of the punch 59 causedby the high-pressure air in the compensation chamber 94. Such acompensation chamber 94 is indeed pressurized to allow the step ofcompressing so as to compensate for the contraction of the melted resinin the molding cavity 41′ during the step of cooling the preform.

During this step, the spool valve 36 inside the hot chamber 30 is opento allow the filling of the tank 72 with the melted resin.

The second step (FIG. 15) is the step of opening the mold and followsthe cooling and maintenance cycle of the preform P. In order to extractthe preform from the cavity 41′, mold 9′ is unblocked by retracting thepneumatic wedge 57 and the lifting of rod 55 along direction D iscarried out. The required opening stroke is always constant, andpreferably of 300-400 mm, e.g. of 330 mm, and does not depend on thetype of molded preform.

At the same time, the dispensing injector 34 must have completed itsloading for the following cycle and the melted resin therein ismaintained at a counter-pressure of about 10 bar due to the thrust ofthe pneumatic cylinder 33 which controls the injector. At the end ofthis second step, the first plate 18 goes into contact with the upperpart of the frame 21: a subsequent lifting of the rod 55 translates intoan opening command of the half-collars 66′, 66″.

The third step (FIG. 16), defined as the first step of extracting thepreform, provides for the detachment of preform P from punch 59 byactuating the half-collars 66′, 66″ which hold the neck of the preformwhile unsticking the latter from punch 59, a few fractions of a secondbefore the half-collars 66′, 66″ are detached from each other in thefollowing step.

The fourth step (FIG. 17), defined as the second step of extracting thepreform, provides for the detachment of the half-collars 66′, 66″ fromeach other and the falling of preform P into the space defined betweenthe closed arms 90′, 90″ of the gripper 4 underneath.

These extraction operations of the preform P include synchronizing, bymeans of electromechanical means, the upward movement of the punch 59with the horizontal opening movement of the half-collars 66′, 66″. Thus,the presence of the gripper 4 (FIG. 15) is ensured under the preformwhen the preform P is released. Subsequently, the displacement of thepreform P by means of the gripper 4 allows to close the cavity 41′ againby lowering the rod 55 in the subsequent step.

In the fifth step, defined as the step of closing mold 9′ and of fillingthe molding cavity 41′, the closing of mold 9′ is completed by means ofthe lowering movement of rod 55 accompanied by the insertion of punch 59and by joining the half-collars 66′, 66″ which couple with the lead-incone of cavity 41′. Once the closing of cavity 41′ has been completed,the pneumatic wedge 57 is inserted in the locking position of mold 9′,impressing a force of about 2-3 t according to needs; this force isadjusted by varying the pressure of the air inserted into the pneumaticactuator 58.

This fifth step corresponds to that shown in FIG. 14 but without thepresence of melted resin in the mold.

Once the closing of mold 9′ has been ensured, the shutter 32 of nozzle31 is opened by means of the actuating device 37. Conduit 70 is closedby valve 36 at the same time as the shutter 32 is opened. The moldingcavity 41′ is thus filled by emptying tank 72. The melted resin entersinto the cavity 41′, pushed by the dual-acting piston 40, impresses anupwards thrust to the punch 59 which retracts because it is held inposition in this instant by a loading spring 63 (FIG. 7 a) of limitedforce of about 200 N. The preform molding cycle is completed and thefirst step described above begins with the introduction of high-pressureair into the compensation chamber 94.

The rotary motion of the various wheels of the plant is synchronized bymeans of electromechanical means, being a very high synchronizationaccuracy necessary for the grippers 4 to be in the correct pickingposition of the preforms P from the molds 9′, 9″, 9′″. The mainembodiment includes the preforms P being extracted by the grippers 4sequentially from each mold in sequence, while the injection of meltedresin in the mold occurs in groups of three, the time offset between theopening of the first molding cavity of a module and the opening of thethird molding cavity of the same module being very short and thusnegligible for the purpose of greater or lesser permanence in the moldand of preform solidification.

In particular, at a circular sector of the rotary carousel 2, e.g. withan angle of about 60° in the middle, there are provided lifting andlowering means (not shown) of the rods 55 of the molds 9′, 9″, 9′″,which enter into said circular sector during the rotation of thecarousel 2 with respect to the axis Y. At the inlet of said circularsector, a rod 55 of the mold 9′ is lifted by means of the wheel ortappet 230 (FIG. 4), which follows a cam surface of said lifting andlowering means of the rod along direction D. Such a cam surface isconfigured to control a vertical upward movement of the rod 55 at theinlet of said circular sector first and then a vertical downwardmovement of the rod 55 at the outlet of said circular sector. The secondstep of opening mold 9′ (FIG. 15), the third step (FIG. 16) and thefourth step (FIG. 17) of extracting preform P from mold 9′ are carriedout during the passage of the mold 9′ along the arc of circumferencedelimiting the aforesaid circular sector. In the described embodiment,where the molding module 9 consists of three molds 9′, 9″, 9′″, eachmolding cycle is applied to a module and three preforms are molded atthe same time. When the molding module 9 passes in the aforesaidcircular sector, three grippers 4 of the transfer star conveyor 50(FIG. 1) enter in sequence into the opening space between the centralpart 13 and the lower part 14 of the corresponding three molds 9′, 9″,9′″ to grip the respective preforms P and transfer them subsequently tothe cooling device 51.

All steps are controlled by appropriate cams (not all of which shown)designed to implement the required movements of all mold components.

The step of cooling preforms P by means of the cooling device 51 isprovided at the end of the molding operations.

In a preferred, but not exclusive embodiment, the number of moldingmodules 9 is from 24 to 32, with a total number of molds 9′, 9″, 9′″between 72 and 96, three molds being provided for each module.

In FIG. 1 the extruder 1, the rotary carousel 2, the transfer starconveyor 50 and the cooling device 51 are arranged substantially in planalong a longitudinal axis. Alternatively, such components may bearranged so as to define in plan an L-shaped configuration or a Z-shapedconfiguration. In all cases, in order to replace the central part 13 ofthe molds, the arm 240 of a robot 250 may act on at least one of the twofree sides of the four sides of the rotary carousel 2 to uncouple thebayonet couplings 15 from the respective rods 55 of the molds of amolding module 9.

In order to allow this uncoupling, a lifting system of the rods 55, e.g.of the pneumatic type, configured to lift the three rods 55 of the threemolds provided in the single molding module 9 together, isadvantageously provided on at least one of the two free sides of therotary carousel 2. Once the rods 55 have been lifted, and thus once themolds have been opened by releasing the central part 13 from the lowerpart 14 containing the molding cavity, it is possible to replace thecentral part 13 with another having, for example, an extension 220 ofdifferent length.

The elements and features shown in the various preferred embodiments ofthe invention may be combined without departing from the scope ofprotection of the invention.

1. A rotary joint for transferring melted plastic from at least oneextruder to a plurality of molds of a rotary machine for moldingpreforms, the rotary joint comprising a fixed structure provided with afixed longitudinal element therein, defining a longitudinal axis Y,wherein a first passage channel is provided within said fixedlongitudinal element, a movable structure adapted to rotate about saidlongitudinal axis Y and adapted to be integrally fixed to the rotarymachine, comprising in turn: a) a first rotary element, arranged abovesaid fixed longitudinal element and adapted to be integrally fixed tothe rotary machine, said first rotary element being provided with asecond passage channel coaxial to said first passage channel, saidsecond passage channel being in communication at a first end thereofwith said first passage channel, and being in communication at a secondend thereof with a plurality of lateral radial channels, said lateralradial channels being provided within said first rotary element, b) asecond rotary element arranged underneath the first rotary element andintegrally fixed thereto, said second rotary element being provided witha central cylindrical through cavity in which a first end of said fixedlongitudinal element is coaxially accommodated, wherein a gap isprovided between the fixed structure and the movable structure, whereina spiral seal is arranged in a part of said gap for ensuring the actionof sealing the melted plastic between said fixed structure and saidmovable structure, wherein said spiral seal comprises a single- ormulti-start spiral groove made on an inner surface of said centralcylindrical through cavity facing a smooth outer surface of said fixedlongitudinal element, said spiral groove being helical and having aninclined helix so as to oppose, with its rotation motion, a naturalexiting direction of a melted plastic flow into the gap.
 2. The rotaryjoint according to claim 1, wherein the helix is inclined by an angle nogreater than 45° with respect to a plane orthogonal to the longitudinalaxis Y.
 3. The rotary joint according to claim 2, wherein said angle isfrom 10° to 40°.
 4. The rotary joint according to claim 1, whereinbetween crests of the spiral groove and the smooth outer surface of thefixed longitudinal element there is a distance of at least 2 mm.
 5. Therotary joint according to claim 1, wherein an upper surface of thesecond rotary element is shaped as a circular crown and is provided witha plurality of radial grooves, equally spaced apart with respect to oneanother.
 6. The rotary joint according to claim 1, wherein said gap isannular in shape, with L-shaped cross section, and is delimited on oneside by a lower surface of the first rotary element and by an uppersurface of the fixed longitudinal element, and on the other side isdelimited by the inner surface of the second rotary element and by anouter surface of the fixed longitudinal element.
 7. The rotary jointaccording to claim 1, wherein a thrust bearing is interposed between themovable structure and the fixed structure.
 8. The rotary joint accordingto claim 1, wherein electrical resistances adapted to keep a meltingtemperature of plastic inside the rotary joint are provided.
 9. Therotary joint according to claim 1, wherein said second rotary element issubstantially bell-shaped.
 10. The rotary joint according to claim 1,wherein the second passage channel has, at the first end thereof, a samediameter as the first passage channel.
 11. The rotary joint according toclaim 1, wherein the first passage channel is considerably longer thanthe second passage channel.
 12. The rotary joint according to claim 1,wherein the first passage channel is adapted to be connected, at a firstend thereof opposite to a second end thereof in communication with thesecond passage channel, to a conduit for feeding melted plastic from theat least one extruder.
 13. The rotary joint according to claim 1,wherein the lateral radial channels are adapted to be connected torespective lateral conduits which connect the first rotary element torespective molding modules of the rotary machine for molding preforms.14. The rotary joint according to claim 3, wherein said angle is from15° and 30°.
 15. The rotary joint according to claim 4, wherein saiddistance is from 3 to 6 mm.